1. Field of the Invention
The present invention relates to an apparatus for bridging an Asynchronous Transfer Mode (ATM) network with Fibre Channel networks to construct an FC/ATM composite network, and a method for detecting abnormalities in the inter-network bridging apparatus and controlling the process of initialization of Fibre Channel networks during the recovery stage.
This application is based on a patent application No. Hei 10-38916 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Asynchronous Transfer Mode (ATM) is becoming the standard choice for a data transfer interface in high-speed broadband networks. Recently, an operating standard for an ATM-LAN network, produced by applying ATM to local area network (LAN), is being developed by an industrial group called the ATM-forum, and in the meantime, for American National Standards Institute (ANSI), operation of a high-speed interface called Fibre Channel, for serial transfer speeds in excess of 1 [Gbps], has been standardized.
Fibre Channel interface will be explained with reference to a protocol stack shown in FIG. 4. Fibre Channel (shortened to FC hereinbelow) refers to a protocol group, which comprises by a physical layer (FC-0), an encoding and decoding layer (FC-1), a frame generation and control layer (FC-2), a common service control layer (FC-3) for such tasks as multiple addressing, a matching layer (FC-4) for interfacing with existing protocols such as small computer system interface (SCSI) or internet protocol (IP). A network based on such protocol groups is the Fibre Channel network referred to FC network. Bridging between the apparatuses based on FC protocol at the level of physical layer and encoding/decoding layer is referred to an FC link. A Fibre Channel network is comprised by a plurality of such FC links.
Data sent from a upper layer protocol such as SCSI and IP to an FC protocol groups are mapped onto variable-length frames. Frame transfer is controlled according to a unit called a sequence which includes more than one frame. If an abnormal event occurs during a frame transfer process, the terminal that detects the abnormal event starts a command sequence in order to abort the offending sequence containing the abnormal frame. Those devices for terminating FC protocols, such as input/output terminals and FC switches, discard all the frames, contained in the offending sequence having the abnormal frame, that may remain in such areas as data transfer buffer.
Next, abnormal detection and notification in FC networks and initialization process for FC links will be explained with reference to FIG. 5, which shows an initialization protocol using ordered sets of codes for FC devices 501, 501' provided with FC protocol for terminating an FC link 502.
FC device 501 in the FC network, detecting a normality recovery in the FC link 502, performs initialization of FC link 502. Initialization process and abnormal detection/notification in the FC network are carried out by the receive/send actions of the ordered sets of codes generated in the encoding/decoding layer in the FC link. In more detail, the FC device 501 sends an special code OLS to the FC device 501' to indicate that it is in an "offline" state ready to carry out the initialization process. Upon receiving OLS code, FC device 501' sends a link reset code LR to FC device 501 to indicate that initialization is being performed. Upon receiving a link reset code LR, FC device 501 sends a link reset response code LRR to the FC device 501', as the response code to link reset code LR. When the link reset response code LRR is received at the FC device 501', the FC device 501' start sending a code Idle, indicating that it is now in a state to enable to transfer data. Upon receiving the code Idle, the FC device 501 similarly becomes ready to transfer data, and start sending a code Idle. Initialization of the FC link 502 is thus completed.
Protocols for Fibre Channels are detailed in "ANSI X3.230-1994, Fibre Channel Physical and Signal Interface (FC PH)" and "Fibre Channel Switch Fabric (FC-SW)".
Next, a conventional FC/ATM composite network, being proposed on a trial basis, comprised by FC networks and an ATM network connected through an inter-network bridging apparatus will be explained with reference to FIG. 6. FIG. 6 shows the configuration of the FC/ATM composite network comprised by terminals 601, 601'; FC switches 602, 602'; inter-network bridging apparatuses 603, 603'; FC links 604a, 604b, 604a', 604b'; FC networks 605, 605'; and an ATM network 606.
If an abnormal event occurs in ATM network 606 during terminals 601 and 601' are in communication, inter-network bridging apparatus 603 detecting the abnormal event generates a signal to indicate that abnormality has been detected in ATM network 606 and, if the ATM network 606 supports an alarm indication function, the ATM network 606 generates the alarm signal to inter-network bridging apparatus 603'. Inter-network bridging apparatus 603', receiving the alarm signal, stops data transfer to ATM network 606. However, in this case, the inter-network bridging apparatus 603' does not notify to the FC switch 602' which is connected through an FC link 604b', because this is a trial network and does not include a response protocol to abnormality.
In the meanwhile, terminal 601 detects a network abnormal event due to the fact that a response frame (ACK) to the dispatched frame does not arrive before timer expiration. Upon detecting the abnormality, terminal 601 starts a command sequence to abort the sequence that includes the frame which has not been acknowledged. In this abort sequence, the terminal 601 sends an abort notification frame to FC switch 602. Upon receiving abort sequence frame, the FC switch 602 discards the data remaining in the data transfer buffer having the sequence that includes the response frame (ACK), and a sequence abort command frame is sent to inter-network bridging apparatus 603. Upon receiving the sequence abort command frame, inter-network bridging apparatus 603 discards the data remaining in the data transfer buffer, similar to the case of the FC switch 602, and sends the sequence abort command frame, through the ATM network 606, to the inter-network bridging apparatus 603'. However, so long as the abnormality is not corrected in the ATM network, the sequence abort command frame cannot reach the inter-network bridging apparatus 603', and therefore, the response frame (ACK) in response to the abort command frame does not arrive at the terminal 601. At this point, terminal 601, the FC switch 602 and the inter-network bridging apparatus 603 start execution of the initialization process of FC network 605, beginning with initialization of FC links 604a, 604b. This action is also taken inside the FC network 605'.
Initialization processes in the FC networks 605 and 605' are undertaken at different times because the timer expiration occurs at different times in the terminals 601 and 601'.
Next, initialization protocol (shortened to init-protocol) in the FC networks 605, 605' will be explained with reference to the flowchart shown in FIG. 7. First, the FC network 605 is initialized by initializing FC link 604a, 604b bridging the devices comprising the FC network 605 (S701). After completing initialization of FC links 604a, 604b, parameters required for communication are exchanged between the FC switches 602, 602'. A timer is used for parameter exchange between FC switches 602, 602' so that, if the necessary parameters are not delivered from the opposing FC switch 602' before the timer expiration, initialization is repeated for the FC links 604a, 604b (S702, S703). These steps complete the initialization of the FC network 605. The FC network 605' is initialized by following a similar process.
However, inter-network bridging apparatuses 603, 603' that have detected a network abnormality or received a notification of abnormality, do not notify FC switches 602, 602' of the abnormal event, because the network is on a trial basis and a response protocol to abnormality has not been included, as mentioned earlier. For this reason, the initialization processes are not executed in the devices affected by the network abnormality until the expiration of the activated timers in the terminal 601 or 601' and the sequence-complete command indicates that abnormality has ended. Even if the abnormality has been recovered, the initializing processes for the FC networks 605, 605' are executed at different times, therefore, parameter exchanges between the FC switches 602, 602' (performed after the FC links 604a, 604b, 604a', 604b' are initialized) are not completed. Thus, initialization of FC links is repeated for each FC network. In this scenario, depending on the initialization time differences among the FC links 604a, 604b, 604a', 604b', separate initialization processes (init-start, timeout, repeat init-start) are continued in individual FC networks 605, 605' such that initialization is constantly being executed in those FC links belonging to either of the two FC networks. The problem is that, because parameter exchange between the FC switches cannot be completed, init-protocol for the FC networks 605, 605' cannot be completed, and communication between the terminals 601, 601' cannot be carried out.
According to the conventional method, therefore, network operations during abnormality and normality recovery cannot be synchronized in a composite network of FC networks bridged by an ATM network. For this reason, depending on the initialization time differences among the FC networks, parameter exchange necessary for communication between the FC switches cannot be performed normally, which means that init-protocol of the FC networks cannot be completed normally and, ultimately, that the communication between the terminals can not be performed normally.